Since you used the SWMBO acronym, that means you've been around the BBS a while so I don't need to point you to this FAQ entry.

Do the rear seat controls just duplicate the steering wheel controls, or is it some kind of dual-zone system where the rear audio is separate from the front audio?

If the former, then if you can get the steering wheel controls working, I'd bet the rear seat controls would work automatically. If the latter, then there's a whole set of complicated issues to work out with amplification and such, and the controls are going to be the least of your worries.